Polysaccharides are becoming increasingly important, as they are materials that can be obtained from renewable raw materials. One of the most frequently occurring polysaccharides is cellulose. Cotton fibers, which consist almost exclusively of cellulose, are an example of the significance of polysaccharides. However, also materials obtained from other cellulosic raw materials, e.g., cellulosic synthetic fibers, are continuing to gain in importance.
The generic names “viscose fibers” and “modal fibers” were assigned by BISFA (the International Bureau for the Standardization of Man-made Fibers) to cellulose fibers produced through chemical derivatization of cellullose with the help of aqueous sodium hydroxide solution and carbon disulfide (CS2).
The name “modal fiber” is a generic term which, as defined by BISFA, stands for a cellulose fiber having a defined high wet strength and an equally defined high wet modulus (i.e., the force required to produce an elongation of the fiber of 5% in its wet state).
However, to date, only one method for the large-scale production of fibers of the viscose and modal types has gained acceptance, namely, the viscose process and variations thereof.
From many patent specifications and other publications, it has generally been known to those skilled in the art for quite some time how this method is carried out. A method for the production of modal fibers is, for example, known from AT 287.905 B.
The big downside of all viscose processes is the use of CS2 that must be recovered with great effort.
The generic name “lyocell fibers” was assigned by BISFA to cellulose fibers produced from solutions in an organic solvent without the formation of a derivative.
However, to date, only one method for the large-scale production of fibers of the lyocell type has gained acceptance, namely, the amine-oxide process. In this method, a tertiary amine oxide, preferably N-methylmorpholine-N-oxide (NMMO), is used as the solvent.
Tertiary amine oxides have long been known as alternative solvents for cellulose. It is known from U.S. Pat. No. 2,179,181, for example, that tertiary amine oxides are capable of dissolving pulp without derivatization and that cellulosic molded bodies, e.g., fibers, can be made from these solutions. U.S. Pat. No. 3,447,939 describes cyclic amine oxides used as solvents for cellulose.
From numerous patent specifications and other publications, it has been known to those skilled in the art for quite some time how this method is carried out. EP 356 419 B1, for example, describes how the solution is prepared, and EP 584 318 B1 describes how such solutions of cellulose in aqueous tertiary amine oxides are spun.
Being a direct dissolving process, the lyocell process is significantly safer from an ecological perspective than the viscose processes, however, it comes with disadvantages in terms of process engineering, as, due to the economic necessity of providing nearly completely closed process cycles, substances may accumulate in the cycles.
U.S. Pat. No. 7,000,000 describes fibers obtained by spinning a solution of polysaccharides which substantially consist of repeating hexose units linked via α(1→3)-glycosidic bonds. These polysaccharides can be produced by bringing an aqueous solution of saccharose into contact with glucosyltransferase (GtfJ), isolated from Streptococcus salivarius (Simpson et al., Microbiology, vol. 41, pp 1451-1460 (1995)). As used in this context, “substantially” means that within the polysaccharide chains there may exist occasional defective locations where other bond configurations may occur. For the purposes of the present invention, these polysaccharides shall be referred to as “α(1→3)-glucan”.
U.S. Pat. No. 7,000,000 first discloses possibilities for the enzymatic production of α(1→3)-glucan from monosaccharides. In this way, relatively short-chained polysaccharides can be produced without the loss of monomer units, as the polymer chains are built from the monomer units. Contrary to the production of short-chained cellulose molecules, the production of α(1→3)-glucan keeps getting less expensive the shorter the polymer chains are, as in that case the required residence time in the reactors will be short.
According to U.S. Pat. No. 7,000,000, the α(1→3)-glucan is to be derivatized, preferably acetylated. Preferably, the solvent is an organic acid, an organic halogen compound, a fluorinated alcohol, or a mixture of such components. These solvents are costly and complex to regenerate.
However, studies have also shown that α(1→3)-glucans dissolve in diluted aqueous sodium hydroxide solution.
Object
In view of such prior art, the object was therefore to provide an alternative direct dissolving process for the production of polysaccharide fibers, which makes do without the CS2 needed in the viscose process and without the effort-consuming closure of cycles of a lyocell process.